linux-kernel - Re: [PATCH][netlabel] Don't risk NULL ptr deref in netlbl_unlabel_staticlist

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Date:	Wed, 16 Apr 2008 17:21:33 -0400
From:	Paul Moore <paul.moore@...com>
To:	Jesper Juhl <jesper.juhl@...il.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH][netlabel] Don't risk NULL ptr deref in netlbl_unlabel_staticlist_gen() if ifindex not found

On Wednesday 16 April 2008 5:08:58 pm Jesper Juhl wrote:
> Hi,
>
> dev_get_by_index() may return NULL if nothing is found. In
> net/netlabel/netlabel_unlabeled.c::netlbl_unlabel_staticlist_gen()
> the function is called, but the return value is never checked. If it
> returns NULL then we'll deref a NULL pointer on the very next line.
> I checked the callers, and I don't think this can actually happen
> today, but code changes over time and in the future it might happen
> and it does no harm to be defensive and check for the failure, so
> that if/when it happens we'll fail gracefully instead of crashing.
>
> Please consider the patch below for inclusion.
>
>
> Signed-off-by: Jesper Juhl <jesper.juhl@...il.com>

I agree we should check for NULL here.  I checked the return of 
dev_get_by_index() in the rest of the file I must have just forgotten 
to check it here.

Thanks for finding this and fixing it.

Acked-by: Paul Moore <paul.moore@...com>

>
>  netlabel_unlabeled.c |    4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/net/netlabel/netlabel_unlabeled.c
> b/net/netlabel/netlabel_unlabeled.c index 4478f2f..6af9457 100644
> --- a/net/netlabel/netlabel_unlabeled.c
> +++ b/net/netlabel/netlabel_unlabeled.c
> @@ -1339,6 +1339,10 @@ static int netlbl_unlabel_staticlist_gen(u32
> cmd,
>
>  	if (iface->ifindex > 0) {
>  		dev = dev_get_by_index(&init_net, iface->ifindex);
> +		if (!dev) {
> +			ret_val = -ENODEV;
> +			goto list_cb_failure;
> +		}
>  		ret_val = nla_put_string(cb_arg->skb,
>  					 NLBL_UNLABEL_A_IFACE, dev->name);
>  		dev_put(dev);

-- 
paul moore
linux @ hp
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